Dolby 7.1

Hey, I just got a Pioneer 7.1 capable reciever and have all the speakers set up, but unfortunately I don't have an HDMI capable projector so I'm using an optical connection right now. I'm under the impression that only HDMI can do 7.1, and optical can only do 5.1 (can it do 6.1? I don't know that at all). Anyways, I was watching 3:10 to Yuma on Blu Ray and it had the option of 7.1 DTS so I picked it anyways. It sounded like it was using all the speakers, but I'm no audio expert. So what was going on? Was it doing 5.1 but just using both sets of surround speakers to kind of fake 7.1? Also, is it better for me to be choosing the actual 5.1 set up option, or should I choose 7.1 anyways considering all of the speakers are set up? Last question, right now when I run a THX audio test off of a DVD using THX it tests all 8 speakers individually. (Does this mean that it actually is recognizing all my speakers and optical can actually do 7 channel surround?) but it says that on 5.1 audio it will use my surround left and right, as opposed to my surround back left/right for those channels. I don't like this because 5.1 is clearly designed to use back channels as back channels, is there anything I can do to change this? Sorry about the length of this post, but I'm clearly in way over my head here. Thanks for any help anyone can provide.